钢筋UHPC梁正截面抗弯承载力计算方法

超高性能混凝土(ultra-high-performance concrete，UHPC)是一种高强、高韧性和高耐久性的新型水泥基复合材料，具有广阔的应用前景。由于UHPC内的钢纤维能有效控制裂缝开展并提高UHPC的抗拉强度，因此，UHPC构件抗弯承载力分析时，一般计入截面受拉区UHPC的抗拉作用，但对于如何考虑受拉区UHPC的抗弯贡献，国内外相关研究结果间存在较大分歧，因此值得进一步研究。首先，编制钢筋UHPC梁正截面抗弯承载力分析程序，分析不同设计参数对截面受拉区UHPC抗弯贡献的影响。结果表明：配筋率、梁高、钢纤维长度、截面形状和预应力水平是影响受拉区UHPC抗弯贡献的主要参数。基于参数分析结果的回归分析，提出截面受拉区UHPC的均匀分布应力折减系数k的计算公式；通过引入受拉翼缘面积折减系数kf，考虑不同截面形状的影响。在此基础上，提出不同弯曲破坏模式下钢筋UHPC梁抗弯承载力的简化计算方法，并以国内外115根钢筋UHPC梁抗弯承载力试验结果验证所提方法的适用性。

Calculation approach for flexural capacity of reinforced UHPC beams

Ultra-high-performance concrete (UHPC) is a newly developed material that has ultra-high strength, high toughness and high durability, and shows a promising prospect in practical applications. Because steel fibers can effectively resist the development of cracks and lead to the increased flexural capacity of reinforced UHPC beams, the tensile capacity of UHPC is usually included in the flexural capability analysis of UHPC members. Nowadays, various calculation methods for determining the flexural capacity of reinforced UHPC beams have been proposed. However, great differences in accounting for the contribution of tensile zone of UHPC in literature can be observed, indicating that further studies shall be necessary. Hence, in this study, the calculation approach of ultimate flexural capacity of UHPC beams was investigated. Firstly, an analysis program of normal-section flexural capacity of the reinforced UHPC beams was used to perform a detailed parametric study. The analysis results showed that the reinforcement ratio, beam height, steel fiber length, prestressing level and cross-sectional shape were the main parameters affecting the flexural contribution of UHPC in the tensile zone. Based on a multiple regression analysis of the numerical results, a unified equation was developed for the tensile strength reduction factor k of UHPC in the tensile zone. By introducing a reduction factor of kf for the tensile flange area, the influence of different cross-sectional shapes was considered. On this basis, a simplified calculation approach for the flexural capacity of reinforced UHPC beams under different flexural failure modes was derived. It was found that the predicted flexural capacities obtained from the proposed approach were in good agreement with available experimental results of 115 reinforced UHPC beams.